1. Field of the Invention
The present invention relates to a fine hole machining method and device for polishing the inner surface of a fine hole such as a ferrule of an optical fiber connector.
2. Description of the Related Art
A ferrule of an optical fiber connector is made of a zirconia-type ceramic material or the like, and a fiber insertion hole with a small diameter is formed in an axial direction thereof. An optical fiber is inserted into the fiber insertion hole and held and fixed thereto. The diameter of the fiber insertion hole is generally 125 to 128 xcexcm, and the roundness of the hole and the taper (sagging) of an edge of the hole are required to be several xcexcm or less.
A hole is formed in a ferrule material (workpiece) using zirconia (ZrO2) by extrusion molding or injection molding. As a fine hole machining method for subjecting the hole to lapping to form a fiber insertion hole, the following methods are known: (1) one taper wire 101 is inserted into a plurality of materials W, W, . . . , relative rotation and relative sliding are given between the materials W, W, . . . , and the taper wire 101, and a plurality of materials W, W, . . . are subjected to lapping together with diamond powder on the periphery of the taper wire 101 (see FIG. 8A) (JP 11-048105 A); (2) the taper wire 101 is inserted into one material W, relative rotation and relative sliding are given between the material W and the taper wire 101, and the hole of the material W is subjected to lapping one by one with diamond powder on the periphery of the taper wire 101 (see FIG. 9) (JP 3062939); and (3) a straight wire 102 is used as a drill, and the hole of the material W is subjected to lapping one by one with diamond powder on the periphery of the straight wire 102 (see FIG. 10).
According to the above-mentioned methods (1) and (2) using a taper wire, the taper precision of the taper wire is required. However, it is difficult to produce a taper wire satisfying such a required precision, which results in degradation of a hole machining precision. In particular, according to the method (1) with high productivity, materials are held on the basis of the outer diameter thereof, and the taper wire is inserted into the materials, as shown in FIG. 8A. Therefore, the taper wire is slightly bent between adjacent materials due to the central shift between the outer diameter of the materials and the holes. Under this condition, the taper wire is provided with tension, and lapping is conducted while relative rotation and relative sliding are performed. Therefore, as shown in FIG. 8B, edge sagging of a hole xe2x80x9cwxe2x80x9d and non-uniformity of the hole xe2x80x9cexe2x80x9d are likely to occur. The central shift of the materials is generally 10 to 20 xcexcm.
According to the method (3) using a straight wire, the hole diameter that can be enlarged by machining is at most about 2 xcexcm. Therefore, although this method can be used for correcting the hole diameter, it is not applicable to machining of the hole of a material into a fiber insertion hole (grinding hem: tens of xcexcm).
Therefore, with the foregoing in mind, it is an object of the present invention to provide a multistage fine hole machining method and device capable of realizing high-precision fine hole machining without edge sagging and non-uniformity of the hole in a short cycle time.
In order to achieve the above-mentioned object, according to the method of the present invention, in a lapping process of passing a wire through a hole of a workpiece and lapping the hole with a polishing material placed between the hole and the wire while the hole and the wire are allowed to be relatively slid, the hole is enlarged, and the workpiece with the hole enlarged is subjected to the lapping process repeatedly to enlarge the hole successively, whereby a desired hole diameter is obtained.
In the above-mentioned method of the present invention, a wire thicker than that in a previous process is used for the workpiece with the hole enlarged or a polishing material with an average particle diameter larger than that of the polishing material used in the previous process is used, whereby the lapping process is repeated.
Furthermore, in the above-mentioned method of the present invention, in a final lapping process, a polishing material with an average particle size smaller than that of the polishing material used in the previous lapping process is used, whereby a machining efficiency and a machining precision can be further enhanced.
According to the above-mentioned method of the present invention, if a hole cleaning process of cleaning a hole of the workpiece that has been machined by lapping in a previous process is provided, and furthermore, a hole diameter inspecting process of inspecting a hole diameter of the workpiece machined by lapping in the previous process is provided, automated fine hole machining that does not require cleaning in the course of machining and labor of inspection can be conducted.
In a device of the present invention, each of a plurality of hole lap stations for enlarging a hole diameter of a workpiece includes: a workpiece holding unit for holding a workpiece; a wire supply unit for supplying a wire; a wire passing unit for passing an end portion of the wire supplied from the wire supply unit through the hole of the workpiece; a tension providing unit for providing tension to the wire passed through the hole of the workpiece by the wire passing unit; a polishing material supply unit for supplying a polishing material to the wire; and a wire/workpiece relative sliding unit for relatively sliding the wire supplied with the polishing material and provided with tension and the workpiece held by the workpiece holding unit. The workpiece with the hole enlarged in one hole lap station is transferred to another hole lap station, whereby the hole is successively enlarged to obtain a desired hole diameter.
In the above-mentioned device of the present invention, the workpiece holding unit can be provided on a workpiece transport device for placing the workpiece at a wire insertion position for passing the wire through the hole and delivering the workpiece from the wire insertion position.
If the workpiece transport device is designed as an index board that performs an index operation between the wire insertion position and the workpiece supply/discharge position, and an inter-station transport device is provided, which transports a workpiece that has been lapped to a hole lap station in a subsequent process at the workpiece supply/discharge position and supplies the workpiece from a previous process, supply/discharge of the workpiece can be automated.
Supply/discharge of a workpiece may also be automated as follows: a plurality of hole lap stations are placed at an equal interval on a circumference, the workpiece transport device is an index table in which a plurality of workpiece holding units are placed so as to correspond to the hole lap stations, and the workpiece holding unit is successively sent to an adjacent hole lap station by an index operation of the index table.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.